With rapid development of information and communications industry, a demand for wireless communication technologies, for example, personal mobile communication, wideband communication, military radar, and the like, is gradually rising. Accordingly, there is an increasing need for a high output and high frequency device with a high level of information processing technology. A gallium nitride (GaN) material that can be used for a power amplifier may be suitable for the high output and high frequency device since the GaN material has properties of a relative great energy band gap, a relatively high heat conductivity, and the like, when compared to conventionally used materials such as a silicon (Si) material and a gallium arsenide (GaAS) material.
A semiconductor device, for example, an aluminum gallium nitride (AlGaN)/GaN heterojunction field effect transistor, may have a high band discontinuity at a junction interface, and a high-density of electrons may be freed in the interface. Thus, electron mobility may increase. However, a defect may be generated on a surface of an AlGaN layer due to a difference between the AlGaN layer and a GaN layer in their lattice constants and thermal expansion coefficients. When a greater amount of Al is included in the AlGaN layer, a density of the defect may increase and an oxygen atom may be included in the surface of the AlGaN layer. In this instance, Fermi-Level-Pinning may occur in a Schottky junction process. Accordingly, when a reverse voltage is applied, a tunneling current may occur on the surface of the AlGaN layer corresponding to a Schottky junction area, due to Fermi-Level-Pinning, and a leakage current may flow.